Leonard's relative, Mark Leonard, lived with his girlfriend, Monserrate Shirley, in the home that exploded.

They were out of town when the explosion occurred.

Witnesses told NBC News they saw police search Bob Leonard's mobile home and were told to go back inside.

Police were looking for a white van that may have been in the area of the explosion on the weekend of the blast.

A neighbor told NBC News that Bob Leonard had a white van parked outside his mobile home for almost two weeks but that he hasn't seen it in the last week and a half.

Monserrate Shirley denied any involvement in the explosion last week during a news conference.

"These people lost their life. I lost my house. Everybody lost their house. It's devastating and people keep asking me questions and questions like I know something. I don't know nothing. I just left my house like we always do," Shirley said.

The Indianapolis Star reported Tuesday that a source close to the investigation said natural gas was intentionally released into the home that exploded. They said they also believe the gas was ignited by a spark that possibly came from a remote source.

Private investigators told NBC the damage caused is too severe to be the result of a natural gas leak.